Life jackets or personal floatation devices are available in many shapes, materials, and designs. Passenger vessels are ordinarily required to carry a sufficient number of life jackets or personal floatation devices to equip each anticipated passenger in the boat. Recreational boaters also carry personal floatation devices with them. As a general rule, personal floatation devices fall into two separate designs.
One design consists of a vest-like design ordinarily made of some inherently buoyant material. Different types of hard or soft foam material, which are ordinarily a polymer material partially filled with gas pockets, which are inherently lighter than water, in part because of the gas pockets contained within the foam material. These devices will ordinarily be worn by someone who is either on, or expects the possibility of, being immersed in water. For example, these life jackets would ordinarily be worn kayakers or water skiers.
A second type of device consists of a more compact molded package in which a particular shape is made of gas impermeable bladder-like construction. Gas is then injected into the bladder-like construction using different expedients. They could be as simple as blowing it up, using a compressed gas cartridge, or using chemical reaction to produce gas, which will then fill the gas impermeable bladder. As a bladder fills with gas, the pressure of the gas is greater than the air outside so the bladder assumes a shape in response to the gas pressure which may resemble the shape of the permanent foam life jackets.
The second type of device will be frequently employed for people who do not anticipate being in the water or, if in the water, do not anticipate the need for any kind of floatation device. Therefore, it is desirable to have a small compact, perhaps concealed, device with them which would only be used in the event of the need of a floatation device.